In human
endometrial cancer, the fourth most common
cancer in women,
tumor suppressor
phosphatase tensin homologue (PTEN) is frequently mutated. In the presence of a mutated
PTEN protein, Akt phosphorylation levels are increased leading to the activation of this survival pathway. Numerous studies indicated that COX-2 is inappropriately induced and up-regulated in a number of malignant
cancer cells. COX-2 plays an important role in
tumor cell biology, taking part actively in angiogenesis particularly via the production of
prostaglandin E2 (
PGE2). The present study was undertaken to determine the involvement of PI 3-K/Akt pathway in the regulation of COXs expression and
PGE2 synthesis. Three different human
endometrial cancer cell lines known to have wild-type PTEN (HEC 1-A) or a mutated inactive
PTEN protein (RL 95-2 and Ishikawa) were used for these studies. Results showed that Akt phosphorylation was high in mutated PTEN cells. RT-PCR studies revealed that Akt1 and Akt2 were the regulated forms whereas Akt3
mRNA was nearly undetectable. COX-2
mRNA expression and
protein levels were high in these cells compared to wild-type PTEN cells as demonstrated by RT-PCR and Western analysis respectively.
PGE2 production was higher in mutated-PTEN expressing phospho-Akt and COX-2 compared to wild-type PTEN cells. Inhibition of PI 3-K with
Wortmannin and
LY294002 blocked Akt phosphorylation and inhibited expression of COX-2 in mutated-PTEN cells. Inhibition of Akt phosphorylation with specific PI 3-K inhibitors and down-regulation of COX-2 increased apoptosis in human
endometrial cancer cells. Likewise, transfection of mutated-PTEN cells with a dominant negative Akt vector, resulted in COX-2 down-regulation and activation of apoptosis, as demonstrated by Hoechst nuclear staining. On the opposite, activation of Akt using a constitutively active expression vector, resulted in the up-regulation of COX-2
protein expression. Specific inhibition of COX-2 with
NS-398 induced apoptosis in COX-2 expressing human
endometrial cancer cells. It is concluded that the PI 3-K/Akt survival pathway is involved in the regulation of COX-2 and
PGE2 synthesis in human
endometrial cancer cells.